As it is well-known, the power delivered by an engine depends on the amount of air fed into the combustion chamber. To increase this power, intake air that is compressed prior to being fed into the combustion chamber of the engine is used. This air, generally referred to as supercharged air, is compressed by any known means such as a turbosupercharger.
As already described in patent application FR-2,781,011 filed by the applicant, the power of a direct-injection supercharged engine can be increased even further by increasing the amount of supercharged air fed into the combustion chamber. The residual burnt gases contained in the combustion chamber are therefore discharged at the start of the intake phase of this engine and replaced by supercharged air. This operation, referred to as burnt gas scavenging, is carried out by overlap of the exhaust and intake valves. At the end of this operation, the intake phase continues, upon closing of the exhaust valves, with an injection of fuel into the combustion chamber.
The claimant has provided for this arrangement within the context of an indirect-injection supercharged engine as better described in French patent application No.02/07,693 filed on 21 Jun. 2002.
The burnt gas scavenging operation is intended to be carried out in this engine by addition of a specific intake means for non-carbureted supercharged air, essentially consisting of a pipe and of a valve. This engine thus comprises a first intake means intended to allow non-carbureted supercharged air to pass into the combustion chamber during the scavenging operation and a second means for allowing carbureted supercharged air to enter the combustion chamber upon closing of the first intake means. Thus, at the start of the air intake phase of the engine, the burnt gas scavenging operation is intended to be carried out by means of an overlap of the exhaust valves and of the non-carbureted supercharged air intake valve. During this overlap, the exhaust valves remain open and non-carbureted supercharged air is allowed to pass into the combustion chamber through the first intake means. The residual burnt gases are thus replaced by non-carbureted supercharged air. At the end of the scavenging operation, the exhaust valves close and carbureted supercharged air is allowed to pass into the combustion chamber through the other intake means that is provided with a fuel injector in case of multipoint fuel injection.
Generally, the free ends of the intake pipes are connected to supercharged air supply means, generally an intake manifold, whose inlet is connected to the outlet of the air compression means.
While the engine is running, the supercharged air which enters the manifold globally supplies all the intake pipes. In this case, there is a risk the carbureted supercharged air and the supercharged air from the non-carbureted air intake pipe may mix. Therefore, when the scavenging operation is carried out at the start of the intake phase, a partly carbureted supercharged air is fed into the combustion chamber, then discharged through the exhaust valves with the burnt gases.
This generates increased fuel consumption and leads to emissions at the exhaust, such as unburnt hydrocarbons.
The present invention is thus intended to overcome the aforementioned drawbacks by means of supercharged air supply means of simple design that prevent fuel bypassing between the two intake means while favouring the acoustics in the manifold.